This study is to determine whether the antibotic, azithromycin, decreases the risk of having a heart attack or other complication related to coronary artery disease in people with heart disease. Azithromycin is an antibiotic that is used to treat infections with a bacteria called Chlamydia pneumoniae. Some studies suggest that Chlamydia pneumoniae infection may be a risk factor for heart attacks and other complications related to coronary artery disease. Chlamydia pneumoniae is spread from person-to-person by sneezing and coughing (unlike a related bacteria, Chlamydia trachomatis, it is not a sexually transmitted disease). Studies show that people who have been infected with Chlamydia pneumoniae in the past have a higher chance of having a heart attack. Other studies show that Chlamydia pnreumoniae is present in the plaque, or material blocking the heart vessel, in many people with heart disease.